Question: Evaluate the expression
\[
  \frac{121 \left( \frac{1}{13} - \frac{1}{17} \right) 
          + 169 \left( \frac{1}{17} - \frac{1}{11} \right) + 289 \left( \frac{1}{11} - \frac{1}{13} \right)}{
        11 \left( \frac{1}{13} - \frac{1}{17} \right) 
          + 13 \left( \frac{1}{17} - \frac{1}{11} \right) + 17 \left( \frac{1}{11} - \frac{1}{13} \right)} \, .
\]
Solution: Let $a=11$, $b=13$, and $c=17$. Using these variables the expression becomes
$$  \frac{a^2 \left( \frac{1}{b} - \frac{1}{c} \right) 
          + b^2 \left( \frac{1}{c} - \frac{1}{a} \right) + c^2 \left( \frac{1}{a} - \frac{1}{b} \right)}{
        a \left( \frac{1}{b} - \frac{1}{c} \right) 
          + b \left( \frac{1}{c} - \frac{1}{a} \right) + c \left( \frac{1}{a} - \frac{1}{b} \right)} \, .$$By grouping all the terms with the same reciprocal together we get
$$  \frac{\frac{1}{a}(c^2-b^2) + \frac{1}{b}(a^2-c^2) + \frac{1}{c}(b^2-a^2)}{\frac{1}{a}(c-b) + \frac{1}{b}(a-c) + \frac{1}{c}(b-a)} \, .$$Using the difference of squares, we can rewrite the numerator of the expression as
$$\frac{1}{a}(c+b)(c-b) + \frac{1}{b}(a+c)(a-c) + \frac{1}{c}(b+a)(b-a).$$Let $S = a + b + c$. Then the numerator is
$$\begin{aligned} &\frac{1}{a}(S-a)(c-b) + \frac{1}{b}(S-b)(a-b) + \frac{1}{c}(S-c)(b-a) \\
&=\frac{1}{a}(c-b)S - (c-b) + \frac{1}{b}(a-b)S - (a-c) + \frac{1}{c}(b-a)S-(b-a) \\
&= \left[ \frac{1}{a}(c-b)+ \frac{1}{b}(a-b) + \frac{1}{c}(b-a) \right]S
\end{aligned}$$But this is just the denominator of our fraction times $S$. So our original expression simplifies to $S$ which is $a+b+c = 11+13+17=\boxed{41}$.